The myrtle warbler (Setophaga coronata coronata) is a small New World warbler.This passerine bird was long known to be closely related to its western counterpart, Audubon's warbler, and at various times the two forms have been classed as separate species or grouped as yellow-rumped warblers, Setophaga coronata. The two forms most likely diverged when the eastern and western populations were separated in the last ice age.